The European Securities and Markets Authority has published all official translations of its final “Guidelines on systems and controls in an automated trading environment for trading platforms, investment firms and competent authorities." This milestone triggers a two-month deadline for national supervisors of countries in the E.U. to either comply or give good reason why they won't.
The rules were first published on Dec. 21, 2011. According to ESMA, national supervisors have to make every effort to comply with the automated trading guidelines. ESMA says that high-frequency trading is one form of automated trading.
For further information, please see the full public statement on the ESMA's website.